JOHANNESBURG, South Africa – Hundreds of thousands of Zimbabweans – orphans and old people, the sick and the down and out – have lost access to food and other basic humanitarian assistance as their government has clamped down on international aid groups it says are backing the political opposition, relief agencies say.

The relief agency CARE has been ordered by the Zimbabwean government to suspend all its operations, which help 500,000 of the country's most vulnerable people. This month, CARE would have fed more than 110,000 people in schools, orphanages, old-age homes and other programs, it said.

Muktar Farah, deputy head of the U.N. Office for the Coordination of Humanitarian Affairs in Zimbabwe, said yesterday that millions of people have lost assistance. “NGOs have been told to scale down or stop operations throughout the country,” he said, referring to nongovernmental organizations.

Zimbabwe's president, Robert Mugabe, speaking yesterday at a U.N. food conference in Rome, accused NGOs of interfering in politics and contended that the West had conspired “to cripple Zimbabwe's economy” and bring about “illegal regime change.”

But Zimbabwean political analysts and civic leaders say Mugabe and ZANU-PF, his governing party, are seeking to use food as a political weapon in a country where hunger afflicts millions. The government recently bought 600,000 tons of corn. By barring NGOs from giving out food in some areas, the governing party controls food distribution and can use it to reward supporters and punish opponents.

On Friday and Monday, representatives of aid groups were summoned by administrators in four districts and instructed to cease all work in the field until a bitterly contested presidential runoff is held June 27 between Mugabe, in power for 28 years, and opposition leader Morgan Tsvangirai.

The U.N. Children's Fund said Monday that 10,000 children had been displaced by pre-election violence and scores beaten. UNICEF said some schools had been taken over by pro-government forces and turned into centers of torture.